Electronic equipment using semiconductor devices are essential for many modern applications. Semiconductor image sensors are commonly involved in electronic equipment used for sensing radiation, such as lights. Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) are widely used in various applications, such as digital camera and mobile phone cameras. The CIS includes an array of pixels located on a substrate. Each pixel includes a photodetector, such as a photodiode or transistor, which absorbs the radiation projected towards the substrate and converts the radiation into an electrical signal.
A back side illuminated (BSI) image sensor device is one type of image sensor device. The BSI image sensor device includes a substrate and a photodetector disposed on a backside of the substrate. Radiation falls directly on the photodetector, rather than passing through a circuitry of the substrate to the photodetector. The radiation sensed by the BSI image sensor device is not disrupted by the substrate.
In the BSI image sensor device, an anti-reflective material is used for absorbing the radiation projected on the device. The anti-reflective material can reduce or prevent a reflection of radiation from its surface and thus an absorption of the radiation by the anti-reflective material can be attained. Further, the anti-reflective material can selectively absorb the radiation in a desired wavelength range.